Field
The disclosure relates in some embodiments to alloys which can be produced using common metal powder manufacturing techniques which serve as effective feedstock in processes such as plasma transferred arc welding (PTA) and laser cladding hardfacing, hardfacing layers and the substrate protected thereby, and methods of making such hardfacing layers.
Description of the Related Art
Hardfacing is the process by which a hard surface coating is applied to a substrate for protection. Typical hardfacing alloys include Chromium Carbide Overlay or CCO. This type of an alloy utilizes a high fraction of chromium carbides, which are relatively hard, to provide protection against wear protection. One drawback of this material is that the material contains hypereutectic chromium carbides which embrittle the material reducing resistance to impact. Similarly, typical hardfacing alloys utilizing hard borides such as SHS9192, manufactured by Nanosteel, contain hypereutectic chromium borides, which again, reduce impact resistance.
Hardfacing materials typically contain carbides and/or borides as hard precipitates which resist abrasion and increase hardness in the alloy. It is well known by those skilled in the art that certain carbides are significantly harder than other carbides. For example, M3C type carbides, which are common in pearlitic steels, have a diamond pyramid hardness (DPH) of about 800-1100 and TiC has a DPH of about 2000-3100. This difference in hardness has a significant effect on the abrasion resistance.
The hardest carbides and borides tend to form at elevated temperatures in a liquid alloy during a potential manufacturing process. In the case of powder manufacturing, high temperature carbide and/or boride is undesirable as these carbides or borides can precipitate on the atomization nozzle and create manufacturing problems that effectively make such an alloy incompatible with that process.
U.S. Pat. No. 8,704,134, hereby incorporated by reference in its entirety, teaches a Fe-based alloy which forms borocarbides among other phases as the principle hard abrasion resistant phases present. Similarly U.S. Pat. App. No. 2007/0029295 and U.S. Pat. Nos. 7,553,382 and 8,474,541, the three of which are incorporated by reference in their entirety, describe alloys where M23(C,B)6 is a fundamental hard phase in the metal structure. In addition, all the alloys disclosed in the above patent references are known to form hyper-eutectic borides.
It is known by those skilled in the art that in typical chromium carbide alloys, that as the carbon and chromium content increases the alloy will move from a hypoeutectic carbide forming space to a hypereutectic carbide space. It is known by those skilled in the art, that increasing boron and carbon has a similar effect. It is not known by those skilled in the art that the M23(C,B)6 phase forms a specific morphology which reduces the resistance of the material to repeated impacts. Moreover, it is not known by those skilled in the art how to specifically control both the carbide and boride fraction in an alloy, such that the carbide and boride fractions can be simultaneously elevated and remain in the hypoeutectic or eutectic regime.